Downhole fluid composition analysis is often used to provide information in real time about the composition of subterranean formation or reservoir fluids. Such real-time information can be advantageously used to improve or optimize the effectiveness of formation testing tools during a sampling processes in a given well (e.g., downhole fluid composition analysis allows for reducing and/or optimizing the number of samples captured and brought back to the surface for further analysis). Some known downhole fluid analysis tools such as the Live Fluid Analyzer (LFA) and the Composition Fluid Analyzer (CFA), both of which are commercially available from Schlumberger Technology Corporation, can measure absorption spectra of formation fluids under downhole conditions. Each of these known fluid analyzers provides ten channels, each of which corresponds to a different wavelength, that correspond to a measured spectrum ranging from visible to near infrared wavelengths. The output of each of the channels represents an optical density (i.e., the logarithm of the ratio of incident light intensity to transmitted light intensity), where an optical density (OD) of zero corresponds to 100% light transmission and an OD of one corresponds to 10% light transmission. The combined optical density output of the channels provides spectral information that can be used to determine the water fraction and composition of formation fluids.
To ensure that a fluid analyzer provides reasonably accurate water fraction and composition information for formation fluids, the fluid analyzer is typically subjected to a calibration procedure that evaluates the baseline drift or error of the fluid analyzer channels at multiple temperatures. The calibration procedure is usually carried out at the surface (e.g., in a laboratory) and is performed at temperatures that may correspond generally to downhole tool temperatures. Additionally, the calibration procedure may involve the use of air, an oil having well-known optical characteristics, and/or water. However, the above-mentioned known calibration procedure may not correct for measurement errors resulting from differences between the conditions under which the calibration was performed (typically a limited number of temperature data points and/or a limited temperature range) and actual downhole conditions, or measurement errors related to fluid analyzer drift or inaccuracy resulting from non-repeatable temperature sensitivity (e.g., drift hysteresis for different temperature cycles) of the fluid analyzer channels.